This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Heat transfer labels are commonly used in the decorating and/or labeling of commercial articles, such as, without limitation, containers for beverages, essential oils, detergents, adverse chemicals, and health and beauty aids. Such articles may include polyethylene, high-density polyethylene (HDPE), low-density polyethylene (LDPE), PET, acrylonitrile, and polypropylene articles. In heat transfer labeling, an ink design overlying a release layer on a carrier (generally referred to as a “carrier web” or “carrier sheet”) is brought into contact with an article to be labeled. When heat is applied to the label, the release layer permits the ink design to be transferred to the article. The release layer may accomplish this by softening and/or becoming molten upon the application of heat, to permit transfer of the ink design. Typically, the release layer is a coating of wax, which is flood coated over one entire side of the carrier, and may serve as a protective layer for the ink design.
Thus, heat transfer labels are multilayered laminates, with each layer having its own function. Heat transfer labels generally include an adhesive layer, an ink design layer, and a release layer (alternatively, an adhesive may be incorporated into the ink design layer, rather than having a separate adhesive layer). The release layer may be a wax release layer, as described above, and is often directly adjacent a surface of the carrier. Thus, the label may be thought to include a “support portion” (e.g., carrier and release layer) and a “transfer portion” (e.g., ink design layer and optional adhesive layer). When subjected to heat, the wax release layer softens, thereby allowing the transfer portion to be separated from the support portion, and the adhesive layer (or adhesive in the ink) adheres the ink design layer to an article being labeled. During this label application, all or part of the wax release layer may transfer with the transfer portion, as well. When some or all of the wax transfers, it may provide protection to the ink design layer. Additionally or alternatively, heat transfer labels may include a separate protective layer (as part of the transfer portion) overlying the ink design layer to protect the ink design layer from abrasion following transfer to an article.
Heat transfer labels are generally provided as a roll or web of labels. During the heat transfer labeling process, the web of labels is subjected to heat, and the label is pressed onto an article with the adhesive layer making direct contact with the article as the web moves past the article (the ink design layer may also make contact with the article, as the adhesive may be part of, and mixed in with the ink of, the ink design layer). As the label is subjected to heat, the wax of the release layer begins to soften and melt so that the transfer portion can be released from the carrier. And, as described above, a portion of the wax release layer may be transferred with the ink design layer. After transfer of the ink design layer to the article, the carrier is removed, leaving the ink design layer firmly adhered to the article. Any portion of the wax release layer that also transfers to the article may serve the purpose of forming a protective layer over the transferred ink design layer. After transfer to the article, any transferred portion of the wax release layer may be subjected to a postflaming technique, which enhances the optical clarity of the wax (thereby enabling the ink design layer therebeneath to be better observed). Such a postflaming process also enhances the protective properties of any transferred wax.
In a typical heat transfer labeling process, the carrier (e.g., sheet of paper) is flood-coated (i.e., substantially entirely coated) with the wax release layer on one side thereof, whereas the ink design layer is printed onto only a portion of the wax release layer. One example of a heat transfer label that has been used to decorate polyethylene (PE) containers includes a paper carrier sheet flood-coated with a wax release layer (approximately 6-8 lbs. wax/3,000 square feet of paper carrier). A protective lacquer layer including a polyester resin is printed on the wax release layer. An ink design layer including a polyamide resin is printed on the protective lacquer layer. A heat-activatable adhesive layer including a polyamide resin is printed on the ink design layer.
The use of a wax flood-coated carrier has at least three disadvantages. First, the application of heat during the transfer process can cause a film of wax to be transferred and deposited over the entire region where the carrier contacts the article being labeled. The deposited wax has a random configuration and is frequently much larger than the ink design, resulting in an expanded and irregular wax “halo” surrounding the design print. This results in a labeled article having an objectionable appearance.
Second, because the ink design is printed only on a portion of the flood-coated wax release layer, the use of such a flood-coated carrier results in a large amount of unused, and thus excess, wax during the labeling process. The use of this excessive amount of wax results in increased costs to the labels. Flood coatings of wax are used for at least two reasons: (1) suppliers of the carrier do not know in advance what ink designs will be applied thereto, and (2) the wax has a high viscosity that does not allow it to be placed on the carrier in a patterned form. More specifically, the label-maker generally does not apply the wax release layer to the carrier itself. Rather, carriers are generally ordered from a supplier and the ink designs are printed thereon by the label-maker at a printing facility. Since the carrier suppliers do not know in advance what ink designs will be applied by the label-maker, they flood-coat the entire carrier with wax to allow for any size, shape, configuration, and registration of ink design. Further, neither the supplier nor the label-maker can apply the wax in a patterned form to a localized area of the carrier (i.e., less than substantially an entire side of the carrier) because the wax formulations used for the wax release layer have a relatively high viscosity, which makes applying a wax release layer that remains localized to a desired specific portion of the carrier difficult. More specifically, wax formulations having relatively high viscosities are difficult to print to a localized area of a carrier because such a wax formulation does not exhibit adequate flow properties, resulting in an unleveled wax release layer which does not exhibit desired performance characteristics. Thus, substantially an entire side of the carrier is flood-coated. The excess amount of wax results in increased cost of the carrier, and thus increased cost of label preparation and of the labels themselves.
Third, the wax release layer on a flood-coated carrier is prone to pinholes, voids, and picking up particulate matter during preparation and shipment of the carrier from the supplier to the printing facility. This results in a certain amount of carrier that cannot be used and must be discarded. This amount can typically be in the range of 15%-20%. Further, the flood coating of wax on the carrier also increases the overall weight of the carrier being shipped, and causes a greater thickness of the support portion (carrier and wax), which results in either (1) less carrier, and thus fewer labels, per roll, or (2) larger rolls of labels. These disadvantages ultimately increase the cost of producing each individual label due to increased waste and increased shipping costs.